Absorbent articles such as sanitary napkins, panty liners, catamenials, incontinence inserts, and/or diapers for adults or babies are commonly provided with an adhesive on their garment-facing surface to facilitate attachment during their usual usage period to a garment of the user. The usual adhesive may be, for example, a pressure sensitive, hot melt, adhesive. These adhesives are typically covered by a release paper or strip prior to use.
Additionally, such absorbent articles can be constructed with adhesive areas that are used to combine the components that ultimately make up part or the whole of the absorbent article. In particular, multi-layer structures forming the top-sheet, core, or back-sheet are often combined by adhesives called construction adhesives.
Typically these absorbent products are made by high-speed machinery. Current machinery includes equipment, such as spray guns or slot coaters that continuously or intermittently add a fluid, such as an adhesive, onto the surface of an absorbent article. Any placement of such a fluid must be done quickly in order to provide high-speed production.
However, current equipment is either inflexible, inaccurate, or both relative to the deposition of the fluid onto the article into the desired pattern of the fluid (adhesive).
For example, hollow drum screen-printing can provide for the creation of a pattern in the screen that can allow for the creation of a desired adhesive pattern. However, adhesive screen-printing is restricted in providing an even, full surface adhesive coverage due to the maximum aperture dimensions and total open area of the a screen relative to the stability of the fluid to be applied.
Other methods can incorporate the use of a gravure, or gravure-like, printing roll. An exemplary gravure printing roll process provides for the rotation of the gravure roll having gravure cells, or indentations disposed upon the outer surface thereof, through a bath containing the fluid (adhesive) which is then placed in contacting engagement with the surface of an absorbent article. The fluid is then transferred to the article from each gravure cell. As mentioned, the gravure roll can contain a specific or desired pattern of cavities upon the surface thereof. Excess fluid placed upon the surface of the gravure roll can be removed by the use of a doctor (i.e., scraper) blade.
While a gravure roll printing process can allow for the application of fluids such as adhesives in patterns on surfaces, the process still has a number of problems associated with it. When applying an adhesive, the gravure roll is continuously supplied with adhesive from an adhesive bath into which the roll is partially submerged and in which it is rotated. Typically, the adhesive must be supplied in a large excess to allow the print roll to rotate through the adhesive bath and become coated with the adhesive. This requires a large amount of energy to be expended particularly in order to maintain the bath and adhesive at the required temperature. Moreover, the rotation of the roll within the bath causes the formation of air bubbles within the adhesive bath that result in the formation of foam. This foam is subsequently transferred to the gravure roll and results in the uneven distribution of the adhesive on the gravure roll surface. This results in the foam-riddled adhesive to consequently be disposed onto the substrate, even after scraping. Furthermore, the foam also collects on the scraper itself and is not readily removable or removed.
Another problem with such a gravure roll printing process is that the amount and distribution of fluid (adhesive) that is deposited from the print roll onto the substrate is extremely difficult to control, resulting in a highly inefficient process. Also, the amount of stringing (i.e. fiberization) of the adhesive during the transfer from the gravure roll to the substrate surface is very large. This results in an irregular application of the adhesive to the surface, in addition to contamination of the adhesive pattern itself. It is believed that it would be beneficial to control a reproduceable application of fluid (e.g., adhesive) from a gravure roll cavity onto a web material or article proximate to a surface thereof.
Some processes could utilize a spraying tool, slot coater, or a series of metering rolls positioned at the right or left hand side of the gravure roll in place of the bath. Such a process continuously applies an amount of adhesive onto a gravure printing roll surface, such that the cavities diposed upon the surface of the gravure roll are filled only to a certain extent. A doctor blade may also be provided to remove any excess adhesive.
Even using the aforementioned adhesive application systems with or without a doctor blade to remove excess adhesive, it has been found that it is difficult to apply sticky, stringy, and viscous adhesives with the precision necessary to provide all cavities of the gravure roll with the required amount of adhesive (e.g. if the volume of all cavities is the same, such that each cavity contains an equal amount of adhesive). This is in particularly the case when the process is performed at a high speed, such as normally necessary in economically feasible production processes, e.g. of more than 20 m/min, or even more than 100 m/min or even more than 150 m/min.
Furthermore, these also require the adhesive to be heated to very high temperatures to be able to spray it onto the surface of a gravure roll, and that the temperature of the adhesive and the roll (or the difference between these temperatures) is difficult to control. Also, slot coaters typically cause the applied adhesive to clump together, seeking to minimize surface area. This results in an uneven application of the fluid to the surface of the gravure roll. Furthermore, the adhesive applied by a slot coater tends to ‘fly off’ the surface of a rotating gravure printing roll after application, especially when the applied adhesive clumps together and/or when they are very hot and more viscous.
Therefore, there exists a clear need to provide an improved (continuous) high speed process to apply fluids (e.g., adhesive) materials to articles in a manner that overcomes the problems associated with the processes discussed supra. There is a clear need to provide a more accurate and efficient way to apply materials including adhesives onto articles, typically in a shaped design to the surfaces of assembled articles from the surface of an exemplary gravure roll. Such a process should allow for the more uniform application of a fluid, either in the form of a uniform layer, or in the form of dots, which have uniformity in the amount of active per dot. Furthermore, such a process should result in a significantly reduced level of contamination by stringing of the viscous material. This can help ensure that the adhesive or other active material is applied exactly as required. Finally, such a process should provide an article with a much more uniformly applied layer or (dot) pattern of the fluid upon the surface of the article.
Additionally, it is believed that there is a need to eject fluid from a gravure roll to minimize any cohesive forces disposed between the surfaces of the fluid and the gravure roll in order to reduce any effects of stringing (i.e. fiberization) of the adhesive during transfer from the gravure roll to a substrate surface.